1) Field of the Invention
The present invention is a dyeing method comprising dyeing an aliphatic polyester filament with a disperse dye by selecting a dyeing temperature, dyeing pH and dyeing time in such a way that an weight average molecular weight of the aliphatic polyester filament to be dyed has a lowering ratio of 20% or less after dyeing.
More particularly, the invention relates to a dyeing method of the aliphatic polyester filament by a disperse dye with good dyeing reproducibility and level dyeing, while substantially maintaining during dyeing the molecular weight and excellent properties of the aliphatic polyester filament. The dyed article obtained by the dyeing method of the invention has a high strength, various hues, and excellent color fastness to light.
2) Description of the Related Art
Conventionally, resins which can be widely used for clothing filaments and films are nylon resin, aromatic polyester resin such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), polypropylene resin and polyethylene resin.
However, filaments prepared from these resins have very slow degradation velocity in the natural environment and thus semipermanently remain when these filaments are subjected to landfill or other waste disposal after use. When plastic prepared from these resins are abandoned, these plastics lead to problems by giving an adverse effect on the scenery and damaging the living environment of marine organisms.
Recently in view of these problems, aliphatic polyester resins which are friendly for the environment have been known as substitutes for these general purpose plastic articles.
The aliphatic polyester resin can be generally degraded with ease. For example, the resin undergoes hydrolysis with relative ease in the presence of water and is also degraded by microorganisms. Thus, the resin can be safely used for filament products, molded articles and other various uses.
When aliphatic polyester resin is used for a filament of clothing, it is desired to dye the filament to various hues in view of appearance and fashion.
Dyeing techniques for an aromatic polyester filament such as PET or PBT have been established for a long time. On the other hand, a dyeing technique for an aliphatic polyester filament remains unknown.
As mentioned above, aliphatic polyester resin is degraded with ease. As a result, when the known and commonly used dyeing technique of aromatic polyester filaments is simply and analogously applied to aliphatic polyester, the dyeing operation is liable to decompose the aliphatic polyester resin and to cause deterioration accompanied by molecular weight reduction.
A report of focusing attention on the ready decomposability of an aliphatic polyester resin and investigating the effect of dyeing conditions such as temperature, time and pH in the dyeing operation of aliphatic polyester filaments on the decrease in the weight average molecular weight of the aliphatic polyester resin after the dyeing operation was not known before the present invention.